This invention relates to water-activatable polymers that are ink jet imprintable and can be used for adhesive image transfer, and constructions made with such polymers.
Labels, tapes and similar constructions are ubiquitous in modem society. Many such constructions include a release liner coated with adhesive, such as a pressure-sensitive adhesive (PSA), which is laminated to a paper or film face stock. Removal of the release liner allows the constructionxe2x80x94face stock coated with adhesivexe2x80x94to be adhered to a substrate.
Most PSAs are tacky when dry and cannot readily be used with ink jet printers. Moreover, such PSAs typically are not hydrophilic, making it difficult to print on them directly with water-based ink jet printer inks. Instead, only the face stock or liner is ink-receptive. The unsuitability of such PSAs for use in ink jet printers is compounded by the tendency of the adhesives to block the printer ports in the printers.
Although attempts have been made to formulate water-activatable adhesives, many of the adhesives produced to date have been rubber-based and, therefore, subject to oxidative and UV degradation. Many rubber-based and other adhesives have been solvent borne, and thus objectional for environmental, health and safety reasons. The following patents are representative. U.S. Pat. No. 3,681,179 to Theissen discloses a solar control film construction having a water-activatable adhesive system comprising a film coated with a normally tacky and pressure-sensitive adhesive, which is covered by a thin, tack-free, continuous water-soluble layer. A tack-free emulsion acrylic adhesive is not disclosed.
European Patents Nos. 199,468 and 297,451 describe a method for compounding water-activatable hot melt adhesives comprising polyaklylenimine or other vinyl heterocyclicmonomers, a hydroxy-substituted organic compound, a plastizier, tackifier, and filler, and an antioxidant. No mention is made of making water-activatable emulsion acrylic adhesives.
U.S. Pat. Nos. 4,331,576 and 4,325,581 to Colon et al. disclose common water-soluble hot melt adhesives based on polymers containing vinyl pyrrolidone and other heterocyclic monomers. Emulsion acrylics are not disclosed.
U.S. Pat. No. 4,052,368 to Morrison and 4,172,824 to Harrington describe water sensitive hot melt adhesives including polyester-based adhesives which typically comprise a copolyester in combination with a plasticizer. The systems are not emulsion acrylics.
None of the above-identified patents disclose or suggest the possibility of making a hydrophilic, acrylic emulsion polymer that is non-tacky when dry and water-activatable to become an adhesive, and that can be used in a xe2x80x9clabel-lessxe2x80x9d or xe2x80x9cliner-lessxe2x80x9d construction, i.e., respectively, a construction in which either a face stock or a liner is not required.
In accordance with the present invention, there are provided water-receptive, water-dispersible, acrylic polymers that are non-tacky when dry but become tacky when wet, and which are particularly useful as water-activatable adhesives for image transfer constructions. In one embodiment of the invention, the composition comprises an acrylic-based polymer prepared by emulsion polymerization of a monomer mixture comprising, based on the total weight of monomers, from about 40 to 70% by weight of one or more alkyl acrylates, the alkyl group of which has from 4 to about 8 carbon atoms; from about 5 to 15% by weight of methyl acrylate; from about 7 to about 17% by weight of vinyl acetate; and from about 10 to 25% by weight of methacrylic acid and/or acrylic acid.
Despite having moderate glass transition temperatures (e.g., from about xe2x88x9220xc2x0 C. to 0xc2x0 C. in some formulations), the polymers can be cast as continuous films that, when dry, are non-tacky to the touch at room temperature, but when exposed to moisture, such as the water in an ink jet printer ink, become tacky. Films cast from the emulsion polymers are water-receptive or hydrophilic, repulpable, water-activatable and transparent to visible light. They can be directly printed upon using a water-based ink and, after activation and adhesion to a substrate, can be removed from a substrate by application of water. They are particularly useful as ink jet-imprintable polymers for convertible, decorative adhesive image sheets and similar constructions, and provide up to 100% image transfer at room temperature, using manual pressure. In contrast, most commercially available image transfer sheets provide no more than about 60 to 80% image transfer.
In another aspect of the invention, an ink jet-imprintable, water-activatable adhesive construction is provided. In one embodiment, the construction comprises at least one layer of water-activatable acrylic polymers, coated on at least one water-impermeable layer, such as a layer of UV varnish, which is applied to a coated or uncoated flexible backing (i.e. a release liner). A continuous, water-soluble, protective detack layer is coated on the water-activatable acrylic polymer layer(s). The water-activatable layer is non-tacky when dry, but becomes tacky when exposed to water. Consequently, when printed with a water-based ink jet printer ink, the detack layer dissolves within the region of the printed image, and the polymer layer(s) become tacky within the region of the printed image, but not in other regions that were not directly printed on. The construction is useful as a label or decorative image sheet, and is applied to an object or surface by adhering the water-activated polymer (which is now tacky) to the object and, removing some or all of the flexible substrate or liner.
Other features and advantages of the invention will become apparent from a consideration of the following detailed description and the accompanying drawings.